U.S. patent application number 13/622344 was filed with the patent office on 2013-06-20 for arrangement for generating fast wavelength-switched optical signal.
This patent application is currently assigned to FREEDOM PHOTONICS, LLC. The applicant listed for this patent is Jonathon Barton, Leif Johansson, Milan Mashanovitch. Invention is credited to Jonathon Barton, Leif Johansson, Milan Mashanovitch.
Application Number | 20130156061 13/622344 |
Document ID | / |
Family ID | 48610097 |
Filed Date | 2013-06-20 |
United States Patent
Application |
20130156061 |
Kind Code |
A1 |
Johansson; Leif ; et
al. |
June 20, 2013 |
Arrangement for Generating Fast Wavelength-Switched Optical
Signal
Abstract
Various embodiments of an arrangement for generating fast
wavelength-switched optical signal are described herein. In some
embodiments, the arrangement can be integrated with lasers, optical
waveguides, optical splitters and gates to form a fast wavelength
switched monolithic optical source. In some embodiments, an optical
modulator is incorporated into the arrangement to form a fast
wavelength switched optical transmitter.
Inventors: |
Johansson; Leif; (Goleta,
CA) ; Barton; Jonathon; (Santa Barbara, CA) ;
Mashanovitch; Milan; (Santa Barbara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Johansson; Leif
Barton; Jonathon
Mashanovitch; Milan |
Goleta
Santa Barbara
Santa Barbara |
CA
CA
CA |
US
US
US |
|
|
Assignee: |
FREEDOM PHOTONICS, LLC
Santa Barbara
CA
|
Family ID: |
48610097 |
Appl. No.: |
13/622344 |
Filed: |
September 18, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61537005 |
Sep 20, 2011 |
|
|
|
Current U.S.
Class: |
372/50.12 |
Current CPC
Class: |
H01S 5/026 20130101;
H04J 14/02 20130101; H01S 5/4087 20130101; H01S 5/0265 20130101;
H01S 5/06216 20130101; H01S 5/40 20130101; H01S 5/0085
20130101 |
Class at
Publication: |
372/50.12 |
International
Class: |
H01S 5/40 20060101
H01S005/40 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED R&D
[0002] This invention was made with Government support under
Contract No. N68335-09-C-0315 awarded by the U.S. Naval Air Systems
Command. The Government has certain rights in the invention.
Claims
1. A fast wavelength switched optical source comprising: At least
one monolithic substrate An in-plane semiconductor laser
monolithically integrated with the substrate, said laser being
fixed wavelength or tunable, and configured to emit optical
radiation from the output reflector along an optical axis A second
in-plane semiconductor laser monolithically integrated with the
substrate, said laser being fixed wavelength or tunable, and
configured to emit optical radiation from the output reflector
along an optical axis An optical combiner element monolithically
integrated with the substrate, with at least 2 input ports and at
least 1 output port, where at least 2 input ports are connected to
the first and second laser, and where the signal from the first and
the second laser are guided to on one or more of the common output
ports
2. The wavelength switched optical source from claim 1, where the
optical combiner element is an active switch
3. The wavelength switched optical source from claim 1, where at
least one of the lasers has an optical gate monolithically
integrated along the optical axis between the laser and the optical
combiner input port.
4. The wavelength switched optical source from claim 1, where at
least one of the lasers has an optical gate monolithically
integrated along the optical axis between the laser and the optical
combiner input port, and the optical combiner element is an active
switch
5. The wavelength switched optical source from claim 1, 2, 3 or 4,
where one output of the combiner/switch is connected to an optical
intensity modulator
6. The wavelength switched optical source from claim 1, 2, 3 or 4,
where one output of the combiner/switch is connected to an optical
phase modulator
7. The wavelength switched optical source from claim 1, 2, 3 or 4,
where two output ports of the combiner/switch each are connected to
a second combiner/switch with at least two input ports, with at
least one output port, and where at least one of the waveguides
connecting said first combiner/switch to said second
combiner/switch contains an optical phase shifter or an optical
phase modulator section.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Application 61/537,005 filed on
Sep. 20, 2011 titled "Arrangement for Generating Fast
Wavelength-Switched Optical Signal," which is hereby expressly
incorporated herein in its entirety.
BACKGROUND
[0003] 1. Field of the Invention
[0004] The embodiments described herein generally relate to
wavelength tunable optical sources used for fiber optic, satellite
and terrestrial communications and sensing applications, and
coherent receivers with monolithically integrated tunable local
oscillator light sources.
[0005] 2. Description of the Related Art
[0006] Several applications require optical sources which have fast
and accurate adjustment of the operating wavelength. One example is
wavelength switched optical sources for use for optical packet
switching applications. In this application, modulated optical data
bits are grouped together in packets and each packet is encoded on
one of many wavelength channels. For the optical source, a
wavelength tuning speed lower than typically 10 ns is required to
change wavelength between optical packets. Required wavelength
accuracy is limited by the requirements of the wavelength division
multiplexing (WDM) architecture used and can in some cases be on
the order of a few GHz.
[0007] Laser wavelength switching speed is limited by several
factors. For a semiconductor laser source, the fundamental limit to
switching speed is laser resonance, typically <1 ns. Efficient
wavelength tuning is often achieved by implementing index tuning in
the laser cavity. For example, index tuning through carrier
injection into semiconductor optical waveguides has a typical time
constant of around 10 ns. Thermal effects will also affect the
index in the laser cavity, with time constants in the microsecond
to millisecond range. Typically, wavelength tuning occurs due to a
combination of several of these effects. As a consequence, the
wavelength accuracy and switching speed are inversely related. No
current optical sources meets the stringent demands for optical
packet switching of a few GHz wavelength accuracy at <10 ns
switching speed.
SUMMARY
[0008] Various embodiments of an arrangement for generating fast
wavelength-switched optical signal are described herein. The scheme
involves at least two optical sources and an arrangement to connect
each of the optical sources to a common output port. The wavelength
tuning range of the two lasers can overlap. The wavelength tuning
range can also not overlap such that the total wavelength tuning
range of the source is greater than that of a single laser. In one
typical mode of operation, the active laser is followed by an
optical gate configured for transmission and is kept at a stable
origin operation wavelength. The second, inactive laser is followed
by an optical gate which is closed and is allowed to be set and
stabilize at a destination wavelength. Wavelength switching is then
performed through rapidly closing the transmitting gate, at the
same time as the closed gate is opened for transmission, switching
the output wavelength of the source from the origin wavelength to
the destination wavelength. This arrangement allows the inherent
limitations in tuning speed and accuracy of a single source to be
overcome by allowing fast optical gates to switch between two
stable lasing wavelengths. In some embodiments, the arrangement can
be integrated with lasers, optical waveguides, optical splitters
and optical gates to form a fast wavelength switched integrated
optical source. In some embodiments, an optical modulator is
incorporated into the arrangement to form a fast wavelength
switched optical transmitter arrangement. In some embodiments, the
arrangement is integrated on a single substrate, forming a
monolithically integrated fast switched optical source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 illustrates an embodiment of the fast switched
optical source incorporating two lasers, and an arrangement for
selectively connect the output from one laser to a common output
port.
[0010] FIG. 2 illustrates output wavelength and optical power as a
function of time for the output from each of the optical gates, and
for the combined output.
[0011] FIG. 3 illustrates an embodiment of the fast switched
optical source incorporating two lasers, two optical gates and an
arrangement to connect each of the outputs from the optical gates
to a common optical output port.
[0012] FIG. 4 illustrates an embodiment of the fast switched
optical source incorporating two lasers, two optical gates and an
arrangement to connect each of the outputs from the optical gates
to a common optical output port and an optical modulator at the
common output port.
[0013] FIG. 5 illustrates an embodiment of the fast switched
optical source incorporating two lasers, two optical gates and an
arrangement to connect each of the outputs from the optical gates
to a common optical output port and an optical Mach-Zehnder
modulator at the common output port.
[0014] These and other features will now be described with
reference to the drawings summarized above. The drawings and the
associated descriptions are provided to illustrate embodiments and
not to limit the scope of the disclosure or claims. Throughout the
drawings, reference numbers may be reused to indicate
correspondence between referenced elements. In addition, where
applicable, the first one or two digits of a reference numeral for
an element can frequently indicate the figure number in which the
element first appears.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] Although certain preferred embodiments and examples are
disclosed below, inventive subject matter extends beyond the
specifically disclosed embodiments to other alternative embodiments
and/or uses and to modifications and equivalents thereof. Thus, the
scope of the claims appended hereto is not limited by any of the
particular embodiments described below. For example, in any method
or process disclosed herein, the acts or operations of the method
or process may be performed in any suitable sequence and are not
necessarily limited to any particular disclosed sequence. Various
operations may be described as multiple discrete operations in
turn, in a manner that may be helpful in understanding certain
embodiments; however, the order of description should not be
construed to imply that these operations are order dependent.
Additionally, the structures, systems, and/or devices described
herein may be embodied using a variety of techniques including
techniques that may not be described herein but are known to a
person having ordinary skill in the art. For purposes of comparing
various embodiments, certain aspects and advantages of these
embodiments are described. Not necessarily all such aspects or
advantages are achieved by any particular embodiment. Thus, for
example, various embodiments may be carried out in a manner that
achieves or optimizes one advantage or group of advantages as
taught herein without necessarily achieving other aspects or
advantages as may also be taught or suggested herein. It will be
understood that when an element or component is referred to herein
as being "connected" or "coupled" to another element, it can be
directly connected or coupled to the other element or intervening
elements may be present therebetween.
[0016] FIG. 1 schematically illustrates an embodiment of an optical
transmitter device. The device comprises at least one
monocrystalline substrate 101, a laser resonator 102, one or more
optical vector modulators 106a and 106b, a polarization rotator 121
and an optical coupler 123. In various embodiments, the various
sub-components of the optical transmitter may be monolithically
integrated with the substrate 101. The optical vector modulators
106a and 106b may include an input waveguide optically connected to
the laser resonator 102, an optical splitter 107, modulation
electrode 109 and an output waveguide. These subcomponents and
other details are provided below. FIG. 1 illustrates the base
arrangement of a fast wavelength switched optical source. The
embodiment of a device, illustrated in FIG. 1, comprises a first
laser 101, laser #1 and a second laser 102, laser #2. Both laser
outputs are connected to an arrangement 103 that can preferentially
select the output from any of the two input ports to form the
optical output signal at a common output port 104. Laser #1 101 and
laser #2 102 can be single wavelength lasers or wavelength tunable
lasers. If these lasers are wavelength tunable, the tuning range of
the first and second laser can overlap such that the total tuning
range of the optical source is equal to that of a single laser. The
tuning range of the first and second laser can also only partly
overlap or not overlap such that the total tuning range of the
optical source is greater than that of a single laser.
[0017] FIG. 2 illustrates one operation example of the fast
wavelength switched optical source. The top graph 201 represents
the lasing wavelength of laser #1 101 and laser #2 102 as a
function of time. Laser #1 is initially set to a stable origin
wavelength while laser #2 is allowed to stabilize at the
destination wavelength. Once laser #2 has reached a stable lasing
wavelength and once after a wavelength switching even, laser #1 is
allowed to deviate from its origin wavelength. The center plot 202
represents the optical power of laser #1 and laser# 2 coupled to
the common output port 104 as a function of time. At a switching
event, the output power from laser #1 is diverted from the output
port, while the output from laser #2 is routed to the output port.
The lower plot 203 represents the resulting wavelength observed at
the common output port 104 as a function of time. The output
wavelength is changed from the stabilized origin wavelength of
laser #1 to the stabilized destination wavelength of laser #2 in
the duration of a switching event.
[0018] FIG. 3 illustrates an embodiment of a fast wavelength
switched optical source. The embodiment of a device, illustrated in
FIG. 3, comprises a first laser 301 lasing at a first optical
wavelength and a second laser 302 lasing at a second optical
wavelength. These lasers can be wavelength tunable. Each of the
lasers is followed by an optical gate, 303 and 304. The function of
these optical gates is to block the output from the laser if
desired. The speed of which the optical gate can be opened up for
optical transmission or be closed to block the output from the
laser is in a typical embodiment faster that the speed one laser
can be adjusted in wavelength from original wavelength to
destination wavelength with sufficient accuracy. Examples of
optical gate implementations include semiconductor amplifiers,
electroabsorption modulators or Mach-Zehnder modulators. The
outputs from the optical gates are connected 305 to a single
optical output port 306. The connection 305 can consist of a
2.times.1 or 2.times.2 optical combiner resulting in an at least
3-dB optical loss, such as a multimode interference coupler, or an
arrangement with equivalent functionality. The connection 305 can
also be implemented as an active optical switch, allowing the
output of one laser to be connected to the common output port with
less than 3 dB of optical loss. The active switch can be
implemented as a 2.times.1 or 2.times.2 Mach-Zehnder interferometer
or any other arrangement of equivalent function. In this variation,
the active switch must be controlled in a synchronized manner with
the optical gates to perform the global wavelength switching
function of the present embodiment. One variation of the embodiment
of FIG. 3 is shown by the alternative arrangement 307 where the
functions of the optical gates 303 and 304, and the connection 305
are combined in a single component 308. This can be a 2.times.1 or
2.times.2 Mach-Zehnder interferometer or equivalent arrangement
where the desired optical input signal can be routed to the common
output port 306 while suppressing other input optical signals.
[0019] FIG. 4 illustrates a further embodiment of the fast
wavelength switched optical source. In this embodiment, the base
arrangement of FIG. 3, 401 is connected to a common optical
modulator 402, capable of changing the phase and/or amplitude of
the common optical output signal. The modulator can be an
electroabsorption modulator, a Mach-Zehnder modulator or any other
modulator structure capable of performing this function. The
optical output signal from the modulator 402 then forms the optical
output port 403 from the fast wavelength switched optical
source.
[0020] FIG. 5 illustrated a variation embodiment of the fast
wavelength switched optical source. In this variation the optical
combiner 501 forming part of the base source configuration 502
illustrated in FIG. 3 is a 2.times.2 type optical coupler which
also forms part of a modulator arrangement 503. In this, the two
output ports from the 2.times.2 coupler 501 are each connected to a
modulator section 504 and 505 that each modulates optical phase
and/or amplitude. These can either be single electrodes, or take
the form of a Mach-Zehnder interferometer. The output ports from
the two modulators 504 and 505 are combined 506 to form a single
common output port 507.
[0021] In the above described embodiments, the fast wavelength
switched source can be assembled by discrete components such as
packaged semiconductor lasers, packaged semiconductor optical
amplifiers and fused fiber couplers. The fast wavelength switched
source can also comprise one or more epitaxial structures formed on
a common monocrystalline substrate. In various embodiments, the
monocrystalline substrate 101 may comprise a single epitaxial
structure. Without subscribing to any particular theory, a single
epitaxial structure refers to a method of depositing a
monocrystalline film on a monocrystalline substrate. In various
embodiments, epitaxial films may be grown from gaseous or liquid
precursors. Because the substrate acts as a seed crystal, the
deposited film takes on a lattice structure and orientation
identical to those of the substrate. In various embodiments, the
epitaxial structure comprises InGaAsP/InGaAs or InAlGaAs layers on
either a GaAs or InP substrate grown with techniques such as MOCVD
or Molecular Beam Epitaxy (MBE) or with wafer fusion of an active
III-V material to a silicon-on-insulator (SOI) material.
[0022] As discussed above in various embodiments, the laser
resonators 101 and 102 may be formed on the common substrate and/or
on the epitaxial structure. In various embodiments, the laser
resonator can include a widely tunable laser. In various
embodiments, the widely tunable laser can comprise a lasing cavity
disposed between two mirrors or reflectors and a tuning section.
The optical radiation or laser light generated by the widely
tunable laser is output from the reflector disposed closer to the
output side of the laser cavity along an optical axis. Without any
loss of generality, the reflector through which laser light or
optical radiation is emitted is referred to as the output reflector
through-out this description. In various embodiments of the optical
transmitter device can be aligned parallel to the crystallographic
axis of the monocrystalline substrate 101.
[0023] In some embodiments, an optical amplifier sections 303 and
304 can be integrated at an output side of the tunable lasers 301
and 302. The optical amplifier sections 303 and 304 can amplify the
optical radiation emitted from the laser resonators 301 and 302 and
in some embodiments, the optical amplifier sections 303 and 304 may
be used to control the power of the generated laser light.
[0024] In various embodiments, the optical radiation from the laser
resonators 101 and 102 can be combined into a single waveguide
using an optical combiner 103. In various embodiments, the optical
combiner 103 can include a multimode interference (MMI) splitter.
In various embodiments, the optical combiner 103 can comprise at
least two input waveguides and at least one output waveguide
configured such that optical radiation propagating through the at
least one input waveguide is coupled to the at least one output
waveguide. In general, integrating a tunable laser with one or more
vector modulators on the same chip may require mitigation of light
reflection. To this effect, in various embodiments, optical
splitters and optical couplers can comprise N inputs and N outputs
that can allow for light evacuation and absorption from the vector
optical modulators when they are in their unbiased or OFF state. In
various embodiments, the combiner 103 can split the light either
equally or unequally between the at least two output waveguides. In
some embodiments, the optical power splitting ratio between the at
least two output waveguide can be tunable.
[0025] In some embodiments the optical signal from the combiner 103
or 305 provides an input to a separate optical modulator 402.
Without subscribing to any particular theory, an optical modulator
may be generally referred to as an optical modulator capable of
modulating either optical intensity and/or optical phase of an
input optical radiation to generate optical modulation.
[0026] In some embodiments, the optical modulator 402 may include
an Electro-Absorption modulator (EAM). In various embodiments, the
optical modulator 402 may comprise a multi branch structure
comprising multiple waveguides. In some embodiments, the optical
modulator 402 may include a Mach-Zehnder modulator (MZM). In some
embodiments, the optical modulator 402 may include a nested dual
Mach-Zehnder modulator. In various embodiments, the optical
modulator can be configured to have low optical transmission in
their unbiased or OFF state (i.e. when no bias voltages are
applied). In some embodiments, this could be accomplished by
varying the width and the lengths of the waveguides associated with
the optical vector modulators or other methods of refractive index
variation between the branches of the optical vector
modulators.
* * * * *